When removing heat from heat sources, for example, when cooling containers with a self-heating content such as concentrated highly radioactive liquids, a convection cooling circuit is often used. The flow of coolant is produced by convection. This affords the advantage that no outside energy is necessary for the purposes of cooling or carrying heat away, and the cooling operation starts up automatically when required.
Such a system operates passively, that is, the system does not need either a drive means or a control means. It is therefore particularly suitable for use in nuclear installations to which access is difficult because of radioactivity.
It has been suggested that the secondary convection cooling circuit be provided with a condenser and an air cooler. In the primary cooling circuit, self-heating of the radioactive concentrate results in the formation of vapor. The vapor is passed into the condenser and cooled down. The condensate is returned to the containers.
In order to ensure a flow of coolant even at low temperatures, frost-protected coolants are used. A coolant such as hexamolar HNO.sub.3 is used which is frost-proof down to -40.degree. Celsius.
The coolant flows through the air cooler and, giving off heat to the outside air, approximately assumes the temperature of the latter. The condenser is therefore supplied with the coolant at the assumed temperature so that the possibility should be considered that the condenser can freeze up in the event of periods of frost which go on for a prolonged period of time. This would prevent the removal of heat via the condenser.